1. Field of the Invention
Embodiments of the invention generally relate to methods and apparatus for modulating of electric field in an electrochemical process. One embodiment of the invention relates to an electrolytic capacitor disposed in an electrochemical processing cell, wherein the electrolytic capacitor is configured to modulate the electric field without inducing deleterious electrochemical reactions.
2. Description of the Related Art
Metallization of high aspect ratio 90 nm and smaller sized features, such as 45 nm, is a foundational technology for future generations of integrated circuit manufacturing processes. Metallization of these features is generally accomplished via an electrochemical plating process. However, electrochemical plating of these features presents several challenges to conventional gap fill methods and apparatuses. One such problem, for example, is that electrochemical plating processes generally require a conductive seed layer to be deposited onto the features to support the subsequent plating process. Conventionally, these seed layers have had a thickness of between about 1000 Åand about 2500 Å; however, as a result of the high aspect ratios of 90 nm features, seed layer thicknesses must be reduced to less than about 300 Å. This reduction in the seed layer thickness has been shown to cause a “terminal effect,” which is generally understood to be decrease in the deposition rate of an electrochemical plating (ECP) process as a function of the distance from the electrical contacts at the edge of a substrate being plated. The impact of the terminal effect is that the deposition thickness near the edge of the substrate is substantially greater than the deposition thickness near the center of the substrate. The increase in deposition thickness near the edge of the substrate as a result of the terminal effect presents difficulties to subsequent processes, e.g., polishing, bevel cleaning, etc., and as such, minimization of the terminal effect is desired.
Attempts have been made to use conventional plating apparatus and processes to overcome the terminal effect through various apparatus and methods. Conventional configurations have been modified to include passive shield or flange members, or segmented anodes configured to control the terminal effect. These configurations were generally unsuccessful in controlling the terminal effect, which resulted in poor control over the deposition thickness near the perimeter.
Active thief electrodes have been used to adjust the current density near the perimeter of a substrate during a plating process to overcome the terminal effect generated by thin seed layers in electrochemical plating processes. An active thief electrode in conventional plating cells is generally configured to pass a current into the solution using an independent power supply. The current passed from the active thief modulates the strength, shape, or direction of the electric field in the solution to achieve desired results. Because a current passes from the thief/auxiliary electrode to the solution, an electrochemical reaction occurs at the interface between the electrode and the solution. This electrochemical reaction may cause several undesired complications. For example, the electrode may need to be cleaned and/or replaced frequently, defects may generate loose metal particles and other products from the electrochemical reaction, and bath additives may be electrochemically broken down.
Therefore, there exists a need for an apparatus and a method for overcoming he terminal effect without unwanted complications during an electrochemical processing.